1. Field of the Invention
The present invention relates generally to the design and use of measuring devices for manufacturing processes in which process parameters must be measured in situ and under the adverse environmental conditions encountered during actual process steps and, more specifically, to the design and use of such measuring devices in the field of semiconductor wafer processing.
2. Description of the Related Art
It is often necessary to make and record measurements of environmental and other parameters during the course of a variety of manufacturing processes in diverse fields. This is particularly true in the field of silicon wafer processing, where variations of physical and chemical parameters across the surface area of a wafer must be held within strict limits in order to insure high process yields. In wafer processing, for example, parameters such as wafer surface temperatures, wafer surface potentials and gas and fluid pressures and flow rates in wafer processing environments must be monitored and the monitoring process should, ideally, provide data that is both an accurate and a reliable function of time.
Unfortunately, the mechanisms for such monitoring are costly and subject to serious limitations. In the case of wafer processing, the processing environment is often characterized by extremes of temperature, the presence of highly reactive gases, fluids and plasmas, mechanical movements such as rapid spinning motions, electromagnetic radiation of various frequencies and intensities and a host of other factors, all of which can adversely affect the performance of sensing mechanisms. In addition, the interconnections between the sensors within the processing environment and the data recording and monitoring mechanisms in the outside world are themselves a problem, as small wires (for example) are fragile while heavy duty interconnects can perturb the system being measured. In the case of spinning wafers, the use of fixed wires is impossible. The frequent necessity of transporting the wafer between different processing areas also places severe limitations on the nature of interconnections.
Another serious problem is the type of sensors available and the manner in which they can be mounted on the wafers themselves. A fairly simple scheme for making temperature measurements involves the fastening of small xe2x80x9ctemperature dotsxe2x80x9d on the surface of a wafer. By means of a phase transition, these dots give an indication of the maximum temperature that they have been subjected to. Unfortunately, the resolution of the dots is poor and it is not possible to obtain a time resolved picture of the temperatures to which the wafer was subjected. Another approach to measuring temperatures involves the mounting of thermocouples to the surface of the wafer. While these are more accurate and can provide time resolution, they require a complex set of wires to an external monitoring station and such wires, as has already been noted, can be a problem.
Virtually all of the more flexible monitoring devices presently in use involve a wafer that is dedicated to process measurements, often called a xe2x80x9csmart wafer.xe2x80x9d The sensing devices are fabricated directly on such a wafer and become a fixed and permanent part of it. Such fabrications often include complex integrated circuitry which is incapable of withstanding the rigorous environments to which actual wafers must be subjected before they themselves have device structures fabricated upon them. Thus, the measurements made by such a sensing wafer cannot adequately simulate the processes to which actual wafers are subjected. In short, such surrogate wafers limit the processes that can be monitored to those processes which the wafer can survive. The use of such smart wafers has been taught in the prior art described below.
Smesny et al (U.S. Pat. No. 5,444,637) provides a semiconductor wafer for sensing one or more processing conditions, such as pressure, temperature, fluid flow rate and gas composition, by placing an equivalent number of sensors within a plurality of regions spaced across the wafer.
Lauf et al. (U.S. Pat. No. 5,969,639) describes a wireless instrumented silicon wafer that can measure temperatures at various points and transmit the temperature data to an external receiver. Such an arrangement is of particular use in a spinning environment.
Flietner et al. (U.S. Pat. No. 6,140,833) provides a semiconductor wafer having at least one processed chip formed directly upon the wafer. The chip includes at least one sensor, a memory storage device, a timing mechanism for providing measured data as a function of time and a self contained power source.
All of the above provided methods and apparatus are subject to limitations imposed by the severity of the processing environment. In particular, at temperatures above 125xc2x0 C. integrated circuitry will not function properly. Environments containing reactive gases and fluids also limit the application of smart wafers and a plasma environment will cause similar problems to those of reactive gases in addition to problems of electromagnetic interference. It is clear that a method and apparatus for in situ measurements is required that can be applied to actual wafers in actual processing environments. It is also clear that it would be highly advantageous if such a method can also be generalized for use in manufacturing processes other than silicon wafer processing. It is to these ends that the present invention is directed.
A first object of this invention is to provide a general method and apparatus for making in situ measurements of process parameters in the adverse environments of certain manufacturing processes.
A second object of the present invention is to provide a method and apparatus for making in situ measurements of an object being processed within an adverse environment wherein the measured parameters include mechanical movement, pressure, temperature, and radiation of various frequencies and intensities.
A third object of the present invention is to provide a method and apparatus for making in situ measurements of an object being processed in an adverse environment so that the measuring, data acquisition and data recording apparatus can reside within the process environment and be thermally insulated from it.
A fourth object of the present invention is to provide a method and apparatus for making in situ measurements of an object being processed in an adverse environment so that the measuring and data acquisition and recording apparatus can reside within the process environment and be electromagnetically insulated from it.
A fifth object of the present invention is to provide a method and apparatus for making in situ measurements of an object being processed in an adverse environment so that the measuring and data acquisition and recording apparatus can reside within the process environment and be isolated from the effects of reactive gases, fluids and plasmas.
A sixth object of the present invention is to provide a method and apparatus for making in situ measurements of an object being processed in an adverse environment so that the measuring and data acquisition and recording apparatus can reside within the process environment and be shielded from electromagnetic radiation of various frequencies and intensities as well as other forms of ionizing phenomena.
A seventh object of the present invention is to provide a method and apparatus for making in situ measurements of an object being processed in an adverse environment so that the measuring and data acquisition and recording apparatus can reside within the process environment and be directly mounted on the object being processed.
An eighth object of the present invention is to provide a method and apparatus for making in situ measurements of an object being processed in an adverse environment so that the appropriate sensors can be either fabricated directly on the object being processed or mounted on the object being processed.
A ninth object of the present invention is to provide a method and apparatus for making in situ measurements in an adverse environment so that said apparatus can be produced independently and used within the processing environment where and when required.
A tenth object of the present method is to provide an apparatus for making in situ measurements in an adverse processing environment so that said apparatus is self contained, lacks connecting cables and is of a size that permits it to be freely and easily transported throughout the entire processing environment.
An eleventh object of the present invention is to provide a method and apparatus for fulfilling all of the objects above that can be applied to the in situ measurement of silicon wafers during silicon wafer processing.
In accord with the objects of this invention there is provided a method and apparatus for in situ measurements, the apparatus in its general form, comprising:
a) a sensor or plurality of sensors that are in contact with the object to be measured either through mounting on or fabrication on said object;
b) a data acquisition system which may further comprise a power supply, a signal conditioning circuit, a microprocessor, a memory, an input/output (I/O) port and a heat sink and wherein a portion of the system may also act as a heat sink;
c) a support board formed of thermally insulating material and covered with radiation reflecting material, said support board providing mechanical support for the data acquisition system and also serving to isolate it from an encapsulating case;
d) a thermal insulation structure that decouples the support board from the encapsulating case and which may further comprise a suspension system;
e) an encapsulating case as already mentioned above, said case containing the data acquisition system, the support board and the thermal insulation structure and said case also providing a vacuum environment or equilibration with an external environment, protection from reactive gases, liquids and plasmas and shielding from external electromagnetic fields and radiation;
f) a plurality of electrical contact pads mounted on the exterior of said case and connected by internal conducting leads to the data acquisition system within the case.